The invention relates to a wheeled vehicle steering system. The term "wheeled vehicle" includes within its meaning motor cars, coaches, lorry cabs and trailers, tractors, trailers and semi-tracked land vehicles.
The system of the invention is particularly suitable for use in wheeled vehicles, such as motor cars, having both steerable front and steerable rear wheels.
Coventional motor cars have steerable front wheels and rear wheels which are not steerable relative to the vehicle body. Such motor cars suffer from a phenomenon known as steering angle slip, in which the angle at which the vehicle steers is less than the angle, known as the steering angle, to which the steerable wheels have been turned when the vehicle is cornering. The angle at which the vehicle steers and the steering angle are measured with respect to a longitudinal axis of the vehicle parallel to the direction of the vehicle tangential to the path followed by the vehicle.
Steering angle slip derives from the fact that the axis of rotation of a conventional motor car is not coincident with its centre of gravity. The driver of a motor car must continuously correct the steering angle in order to ensure that the vehicle follows the path which he intends it to. The vehicle steering system is therefore an open-loop, mechanical system.
There is therefore a need for a wheeled vehicle steering system of greater accuracy than known steering systems having open-loop control.